Cathodic protection circuit including diode means



July 11, 1967 s. D. WARNER 3,

CATHODIC PROTECTION CIRCUIT INCLUDING DIODE MEANS Filed May 20, 1965 SACFHFICIAL sgfifigg PROTECTED ANODE DROP DEVICE -2 e MAGNESIUM SHIPS ANODE HULL \2 DIODE 3 sEA WATER ,V

EARTH\/ MAGNESIUM g g ANODE N22 A.- V A; V 9 2| l/ l/ l\ \l\ 2 lvlvlvl'L INVENTOR.

STANLEY D. WARNER Agent United States Patent Orifice 3,330,751 Patented July 11, 1967 3,330,751 CATHODIC PROTECTION CIRCUIT INCLUDING DIODE MEANS Stanley D. Warner, Upland, Calif., assignor to Lockheed Aircraft Corporation, Los Angeles, Calif. Filed May 20, 1963, Ser. No. 281,577 4 Claims. (Cl. 204-196) This invention relates to cathodic protection systems and more particularly to an automatically controlled sacrificial anode anticorrosion system.

Corrosive effects which occur due to electrolytic action when two dissimilar metals are immersed in an electrolyte are well-known. Prior protective systems to counteract the corrosive effects have been of two basic types, viz., sacrificial anode and impressed current or combinations of these two. The present invention is concerned primarily with the former type.

Generally, the corrosion problem exists not as a typical galvanic cell, but wherever a metal is wetted by an electrolyte, whether a liquid or gas, and the earth is wetted by the same electrolyte. Cathodic protection makes use of the fact that metals may be arranged in the familiar voltaic or electro-chemical series, the position of any given metal in the series being determined by the direction of flow of current through the electrolyte from that metal to any other in the series, when the two metals are connected exteriorly of the electrolyte. The metals higher in the series are regarded as electro-positive or anodic with respect to the others and the metals lower in the series are regarded as electro-negative or cathodic.

An object of the present invention is to provide cathodic protection without the need for external power.

A further object of the present invention is to provide automatically controlled cathodic protection utilizing sacrificial anodes.

A further object of the invention is to provide accurate and uniform polarization control which eliminates the need for manual adjustment.

These and other related objects will become more apparent from the following detailed description when taken in connection with the accompanying drawings, wherein:

FIGURE 1 is a schematic representation of the invention.

FIGURE 2 is a schematic representation of a specific embodiment of the invention.

FIGURE 3 is a schematic variation of the embodiment shown in FIGURE 2.

The invention may be broadly regarded as comprising a constant voltage device connected in series with the surface to be protected, the sacrificial anode and the electrolyte. Variations of the invention may include various series and/or parallel connections of constant voltage devices, with or without amplifiers and reference cells.

With reference now to the drawings, FIGURE 1 shows the invention in its basic or simplest form. A- metal surface 1 such as a ships hull which is to be protected is immersed in a liquid or electrolyte. In the absence of cathodic protection, the ships hull corrodes due to the electron loss to the electrolyte or sea water to the earth or ocean bottom in this case. This electrolytic action is reversed in cathodic systems by utilizing a metal which is anodic or higher in the electrochemical series. In FIG. 1 a sacrificial anode 2 is electrically connected to the metal surface 1 through a constant voltage drop device 3. As a result the metal surface becomes cathodic, and erosion of the surface by electron loss ceases.

In order for the metal surface to be fully protected from corrosive electron loss, the metal must be maintained cathodic or slightly negative with respect to the so-called polarization voltage. For steel, as an example, the polarization voltage is around 600 mv. Therefore, in series path of FIG. 1 the metal of the sacrificial anode and the selection of the constant voltage drop device will determine the range of potential within which the cathode surface is maintained.

For illustration purposes and with reference to FIG. 2, the magnesium anode and the silicon diode provides a range of about 810 to 850 mv. in the cathode potential. Other anode materials may be utilized or other diodes taken single or in series and/ or parallel combinations may be used to provide other ranges of cathode potential.

The uniqueness and simplicity of the invention should be readily apparent. By utilizing a constant voltage drop device the cathode potential is maintained essentially constant. The galvanic voltage from the sacrificial anode due to the electro-chemical action provides the DC. power for polarization without the need of a separate external power source. In addition the sacrificial anode in FIGS. 1 and 2 functions as a sensing or reference anode as well as the polarizing anode.

Now with reference to FIG. 3, the inventive concept is illustrated in connection with a reference cell such as the well-known silver-silver chloride cell. In this case a constant voltage drop device 23 is connected in series with the reference cell 24 and the input to a transistor amplifier 25. It is to be understood that other conventional reference cells may be utilized. The potential of the reference cell with respect to the steel hull 21 is essentially uniform. Since the voltage applied to the amplifier input is the difference between the uniform cell potential and the constant voltage drop across the diodes 23, then it is believed apparent that this difiference will be constant or effectively regulated and the amplifier output will be highly stabilized and uniform. Thus, a protective potential exists between the sacrificial type magnesium anode 22 and the steel hull 21 such that no corrosion takes place on the cathodic hull. As with FIGURES 1 and 2, the potentials utilized are generated within the cathodic system itself by chemical action eliminating the need for an external power source.

The major advantage of this system as compared to FIGS. 1 and 2 is the superior reference cell (Ag-AgCl) and the resulting improvement in the accuracy with which the desired polarization potential can be maintained.

While specific embodiments of the invention have been shown and described it should be understood that certain alterations, modifications and substitutions may be made to the instant disclosure without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. In an electrolytic system for cathodic protection of the type which includes an electrolyte, an electrode adapted to be immersed in the electrolyte, a cathode structure to be protected adapted to be immersed in the elecrolyte, said electrode being formed of a material higher in the electrochemical series than said structure, diode means having a consultant voltage drop conductively connected between said electrode and said structure, said system consisting solely of the series connection of said electrode, said constant voltage device, said structure and the electrolyte whereby a substantially constant polarization potential is developed between said electrode and said structure.

2. The electrolytic system as defined in claim 1,

wherein said electrode is a magnesium sacrificial anode.

3. In an electrolytic system for cathodic protection of the type which includes an electrolyte, the combination comprising a structure to be protected adapted to be immersed in the electrolyte, a sacrificial anode adapted to be immersed in the electrolyte, a reference electrode adapted to be immersed in the electrolyte, a diode means having a constant voltage drop, an amplifier means including a portion of said amplifier for connecting said diode means between said structure and said reference electrode, means including a second portion of said amplifier for connecting said anode to said structure.

4. An electrolytic system as defined by claim 3 wherein the reference electrode is of the silver-silver chloride type and the amplifier is a transistor amplifier.

Sands 204231 Blake et a1. 136100 Andrus 204196 Sabins 204-197 Moore 32225 Sabins 204-496 Bradley 204196 Ruetschi 320-13 Holm et a1.

Fischer 204-196 Husock 204196 Oster.

Ballard.

Byrne 204-4196 JOHN H. MACK, Primary Examiner.

20 T. H. TUNG, Assistant Examiner. 

1. IN AN ELECTROLYTIC SYSTEM FOR CATHODIC PROTECTION OF THE TYPE WHICH INCLUDES AN ELECTROLYTE, AN ELECTRODE ADAPTED TO BE IMMERSED IN THE ELECTROLYTE, A CATHODE STRUCTURE TO BE PROTECTED ADAPTED TO BE IMMERSED IN THE ELECTROLYTE, SAID ELECTRODE BEING FORMED OF A MATERIAL HIGHER IN THE ELECTROCHEMICAL SERIES THAN SAID STRUCTURE, DIODE MEANS HAVING A CONSULTANT VOLTAGE DROP CONDUCTIVELY CONNECTED BETWEEN SAID ELECTRODE AND SAID STRUCTURE, SAID SYSTEM CONSISTING SOLELY OF THE SERIES CONNECTION OF SAID ELECTRODE, SAID CONSTANT VOLTAGE DEVICE, SAID STRUCTURE AND THE ELECTROLYTE WHEREBY A SUBSTANTIALLY CONSTANT POLARIZATION POTENTIAL IS DEVELOPED BETWEEN SAID ELECTRODE AND SAID STRUCTURE. 